diff options
| -rw-r--r-- | src/corelib/kernel/qabstracteventdispatcher.cpp | 30 |
1 files changed, 24 insertions, 6 deletions
diff --git a/src/corelib/kernel/qabstracteventdispatcher.cpp b/src/corelib/kernel/qabstracteventdispatcher.cpp index e79f87a..cc08f092 100644 --- a/src/corelib/kernel/qabstracteventdispatcher.cpp +++ b/src/corelib/kernel/qabstracteventdispatcher.cpp @@ -137,6 +137,12 @@ void QAbstractEventDispatcherPrivate::init() // free list). As an added protection, we use the cell to store an invalid // (negative) value that we can later check for integrity. // +// ABA prevention simply adds a value to 7 of the top 8 bits when resetting +// nextFreeTimerId. +// +// The extra code is the bucket allocation which allows us to start with a +// very small bucket size and grow as needed. +// // (continues below). int QAbstractEventDispatcherPrivate::allocateTimerId() { @@ -164,6 +170,8 @@ int QAbstractEventDispatcherPrivate::allocateTimerId() newTimerId = prepareNewValueWithSerialNumber(timerId, b[at]); } while (!nextFreeTimerId.testAndSetRelaxed(timerId, newTimerId)); + timerId &= TimerIdMask; + timerId |= b[at] & TimerSerialMask; b[at] = -timerId; return timerId; @@ -174,12 +182,13 @@ int QAbstractEventDispatcherPrivate::allocateTimerId() // X[timerId] = nextFreeTimerId; // then we update nextFreeTimerId to the timer we've just released // -// The extra code in allocateTimerId and releaseTimerId are ABA prevention -// and bucket memory. The buckets are simply to make sure we allocate only -// the necessary number of timers. See above. -// // ABA prevention simply adds a value to 7 of the top 8 bits when resetting // nextFreeTimerId. +// +// In addition to that, we update the same 7 bits in each entry in the bucket +// as a counter. That way, a timer ID allocated and released will always be +// returned with a different ID. This reduces the chances of timers being released +// erroneously by application code. void QAbstractEventDispatcherPrivate::releaseTimerId(int timerId) { int which = timerId & TimerIdMask; @@ -187,12 +196,21 @@ void QAbstractEventDispatcherPrivate::releaseTimerId(int timerId) int at = bucketIndex(bucket, which); int *b = timerIds[bucket]; - Q_ASSERT(b[at] == -timerId); +#ifndef QT_NO_DEBUG + // debug code + Q_ASSERT_X(timerId == -b[at], "QAbstractEventDispatcher::releaseTimerId", "Timer ID was not found, fix application"); +#else + if (timerId != -b[at]) { + // release code + qWarning("Timer ID %d was not found, fix application", timerId); + return; + } +#endif int freeId, newTimerId; do { freeId = nextFreeTimerId;//.loadAcquire(); // ### FIXME Proper memory ordering semantics - b[at] = freeId & TimerIdMask; + b[at] = prepareNewValueWithSerialNumber(-b[at], freeId); newTimerId = prepareNewValueWithSerialNumber(freeId, timerId); } while (!nextFreeTimerId.testAndSetRelease(freeId, newTimerId)); |